1. Field of the Invention
The present invention relates to a spin-valve magnetoresistive element, in which electrical resistance changes with the magnetization vector of a pinned magnetic layer and the magnetization vector of a free magnetic layer affected by an external magnetic field. In particular, the present invention relates to a spin-valve magnetoresistive element capable of suppressing the Barkhausen noise by a stable bias magnetic field applied to the free magnetic layer.
2. Description of the Related Art
FIG. 4 is a sectional view of a prior art spin-valve magnetoresistive element or spin-valve magnetoresistive head which detects a recording magnetic field from a hard disk. An antiferromagnetic layer 11, a pinned magnetic layer 2, a non-magnetic electrically conductive layer 3, a free magnetic layer and a protective layer 8 are formed on an underlayer 7 in that order, and hard biasing layers 6 are provided on both sides of these layers.
In general, the antiferromagnetic layer 11 is constructed of an iron-manganese (FeMn) alloy, the pinned magnetic layer 2 and the free magnetic layer 4 are constructed of an iron-nickel (FeNi) alloy, and the hard biasing layers are constructed of a cobalt-platinum (CoPt) alloy. The underlayer 7 and the protective layer 8 are constructed of nonmagnetic materials, such as tantalum.
In the production of the spin-valve magnetoresistive element shown in FIG. 4, the six layers from the underlayer 7 to the protective layer 8 are formed, the portions at both sides of the six deposited layers are removed by an etching process, such as an ion-milling process, so as to form slanted side faces, and the hard biasing layers 6 are formed on the slanted side faces. Each hard biasing layer 6 has a horizontal surface 6' parallel to the other layers and a slanted surface 6" according to the above-mentioned slanted side faces. The hard biasing layer 6 has a constant thickness h1 at the horizontal surface portion, and a decreasing thickness at the slanted surface portion.
The pinned magnetic layer 2 comes into contact with the antiferromagnetic layer 11 and is put into a single magnetic domain state by an exchange anisotropic magnetic field which is generated by an exchange coupling at an interface with the antiferromagnetic layer 11 to fix the magnetization vector in the Y direction. On the other hand, the magnetization vector of the free magnetic layer 4 is fixed in the X direction by the effect of the hard biasing layer 6 which is magnetized in the X direction.
In the spin-valve magnetoresistive element, electrically conductive layers 10 are formed on the hard biasing layers 6 with intermediate layers 9 formed therebetween, and the electrically conductive layers 10 supply a sensing current to the pinned magnetic layer 2, the nonmagnetic electrically conductive layer 3 and the free magnetic layer 4. The magnetic recording medium, such as a hard disk, scans in the Z direction. When a leakage magnetic field from the magnetic recording medium is applied to the free magnetic layer 4 in the Y direction, the magnetization vector of the free magnetic layer 4 varies from the X direction to the Y direction. The electrical resistance depends on the variation in the magnetization vector in the free magnetic layer 4 and the magnetization vector in the pinned magnetic layer 2, hence the leakage magnetic field from the magnetic recording medium is detected by the variation in the voltage due to the variation in the electrical resistance.
Although, in the prior art spin-valve magnetoresistive element, the pinned magnetic layer 2, the nonmagnetic electrically conductive layer 3 and the free magnetic layer 4 have relatively small thicknesses, while the antiferromagnetic layer 11 has a noticeably large thickness. For example, the pinned magnetic layer 2, the nonmagnetic electrically conductive layer 3 and the free magnetic layer 4 have thicknesses of 100 angstroms or less, and the antiferromagnetic layer 11 has a thickness of approximately 300 angstroms. As a result, the hard biasing layer 6 lies below the free magnetic layer 4 which is formed above the thick antiferromagnetic layer 11, and thus the horizontal surface 6' of the hard biasing layer 6 lies below the bottom face of the free magnetic layer 4. The side faces of free magnetic layer 4 barely come in contact with the thin slanted portion of the hard biasing layer 6.
Although the hard biasing layer 6 is magnetized in the X direction by the coercive force, the slanted portion of the hard biasing layer 6 cannot not apply a sufficient bias magnetic field in the X direction to the free magnetic layer 4 due to the small thickness of the slanted portion in the X direction. As a result, the magnetization vector of the free magnetic layer 4 is barely stabilized in the X direction, hence Barkhausen noise will occur.